Ship having an air cushion under the bottom



June 13, 1961 K. F. GRAM 2,988,035

SHIP HAVING AN AIR CUSHION UNDER THE BOTTOM Filed Dec. 12, 1957 Patented June 13, 1961 ice 2,288,035 SHIP HAVING AN AIR CUSHION UNDER TIE BOTTQM Kniid Fini Gram, Ordrup Have 3, Ch., Copenhagen, Denmark Filed Dec. 12, 1957, Ser. No. 702,432 Claims priority, application Denmark Dec. 27, 1956 2 Claims. (Cl. 11467) The invention relates to a ship having an air chamber at the bottom thereof extending in both longitudinal and transverse direction and being open at the bottom thereof, said air chamber being provided with air inlets at the fore end and air outlets at the aft end, and means for forcing air through the air inlets to the air chamber in adjustable quantities, so as to produce a longitudinal air flow in the air chamber.

, In ships of the kind described side keels or the like are used to limit the air chamber at the sides. These side keels can prevent air losses to the water in the port or starboard side, but only if the angle of heel of the ship is very small. If the ship has a constant angle of heel greater than one degree or, especially, if the ship is rolling, great air losses will occur at the side edges of the air chamber whereby the air chamber will be partly or in most cases nearly completely filled with water, so that the skin friction against the ships bottom is greatly increased, though it is the purpose of the air chamber to reduce the skin friction.

This serious drawback which has hitherto made the use of air chambers impossible in practice, is completely eliminated in astonishing manner if according to the present invention the air chamber has additional air inlets and air outlets at the port and starboard edges of the air chamber, and independent means for forcing a stream of air through either the port or the starboard air inlets so as to produce a transverse air flow in the air chamber.

When for instance the starboard side of the air chamber is deeper immersed than the port side, the air in the air chamber will flow very rapidly from starboard to port, and in this case air is forced through the starboard inlets and is taken out through the port outlets. In this way it is possible, even during rolling of the ship, to maintain a nearly complete air cushion, i.e. and air layer covering the full breadth of the air chamber which may also be called the air lubricated area. If the angle of heel is constant in time, the transverse air velocity must of course also be constant, and if the ship is rolling, the transverse air velocity must be increased, decreased and reversed periodically. The longitudinal and the transverse air flow will together produce an oblique air flow lying at right angles to the isobar curves which can be drawn through points of same pressure in the bottom plane of the ship.

The present invention is not concerned with the control of the transverse or the longitudinal air flow, as this control may be carried out by any suitble means, known per se. However, it is suggested to use automatic control means governed for example by the angle of heel and the pitch angle, respectively. It will also be noted that the intake of the air forcing means need not be connected to the atmosphere, but may be connected with the corresponding air outlets, whereby two independent air circulating systems (a transverse and a longitudinal one) are obtained, each of them being closed to the atmosphere, so that the energy for compressing atmospheric air up to the pressure at the bottom of the ship, is saved. This principle, however, is known from the earlier ships with longitudinal circulation only.

If the ship has an anti-rolling tank, formed as a U-tube containing water closed at its free upper ends, aim of power for forcing the air through the inlets and sucking it out through the outlets may be obtained free of charge from this anti-rolling tank. This is according to the invention done in the way that the air space above the water in one of the tank legs is connected with the air chamber at one side edge, whereas the air space of the other tank leg is connected with the air chamber at the other side edge. When during rolling the water in the tank legs is rising and falling, air will be alternately forced into and removed from for instance the starboard side of the air chamber, and this will take place exactly with the period of the rolling.

Of course this tank arrangement is of no use when the ship has a constant angle of heel or trim, so it is advisable to combine the tank arrangement with mechanical air forcing means, such as blowers.

The more detailed arrangement of air pipes, valves, automatic governing means for the same, as well as the arrangement of the U-tube tanks, if such are employed, will be easy to work out for a person skilled in the art, so that the present invention is exclusively an invention of a principle for air-lubricating ships which is now clearly and definitely defined in claim 1 appended hereto.

In the drawing is illustrated different Ways of carrying out the invention, whereby FIG. 1 is a longitudinal section of a ship having a longitudinal air circuit,

FIG. 2 is a midship section of a ship having a transverse air circuit driven by mechanical power, and

FIG. 3 is a midship section of another ship with a transverse air circuit driven by a system of anti-rolling tanks.

The ship shown in FIG. 1 has a bottom 1 the fiat portion of which is joggled upwards so that an air chamber 2 is formed. From the aft part of the air chamber 2 an air duct 3 is led upwardly above the waterline VL and therefrom in a forward direction to the suction side of a blower 4. From the delivery side of the blower 4- a corresponding air duct 5 is led down to the front portion of the air chamber 2.

When the blower 4 is in operation, an air flow is produced in the closed circuit having the direction indicated by the arrows. The air in the air chamber 2 must have a velocity astern only a little less than the speed of the ship through the water.

To the air duct 3 is connected a pressure pipe 6 belonging to a small compressor 7 taking in from the atmosphere. The compressor 7 serves to cover accidental air losses from the air chamber 2 to the water.

The ship according to FIG. 2 has ordinary flat bottom 1 with an air chamber 22 limited by side keels. An air pipe 23 debouohes into the starboard side of the air chamber 22 and is at the other end connected to a reversible gear pump 24 from which another air pipe 25 leads to the port side edge of the air chamber 22. The closed air circuit 22, 23, 24 25 can be supplied with fresh air, when necessary, through a pipe 26 connected to a small compressor 27 which takes air in from the atmosphere.

The ship in FIG. 2 is shown with a heel to port, whereby the air in the air chamber 22 is moving rapidly to starboard on account of the buoyancy acting on the air. However, when the pump 24 is Working to force the air in the direction shown by the arrows, air will continuously be supplied to the port side and removed from the starboard side of the air chamber, so that air chamber 22 will not be partly or completely filled with Water, as would otherwise be the case. If the ship takes a roll to starboard, the gear pump 24 must be reversed.

The transverse air circuit shown in FIG. 2 is used in connection with the known: longitudinal air circuits described in the foregoing. The transverse air circuit will only be in operation when the ship is rolling or has any constant angle of heel, i.e. in the cases where the air 3 chamber would otherwise be filled with water through escaping of air along the port or starboard side keels.

FIG. 3 shows another embodiment of the transverse air circuit driven by anti-rolling tanks instead of by mechanical power. Above the air chamber 2 is arranged an ordinary bottom tank 8. Between the bottom tank 8 and each of the'ships sides 9 is arranged a small antirolling tank consisting of two tank'legs 10 and 11 and a vertical air duct 12 which is connected with the top of the corresponding tank leg 11. From the tank leg 10 of the port tank an duct 13 is led up over the waterline VL across the ship and down again to the top of the tank leg 10 of the starboard tank. In the air duct 13 is inserted a regulating valve 14.

In FIG. 3 the Water in the anti-rolling tanks is shown in an end position in which the water velocity is Zero. As the phase displacement between the tanks and the ship is, as usual, about 90, the ship is simultaneously on even keel, as shown. A little later, the water in the tanks and thereby the airin the transverse circuit will move in the direction indicated by the arrows, which corresponds to a beginning inclination to port. A quarter of an oscillation period later the roll angle will be maximum and the water surfaces in the tank legs 10 and 11 be in alignment, whereby the water velocity and thereby also the air flow velocity will have its maximum value.

The circuit shown in FIG. 3 is driven by the rolling of the ship and is thus unable to compensate for a constant angle of heel when the ship is sailing in still water. The air velocity can be controlled by means of the valve 14.

I claim:

1. Ship having an air chamber at the bottom thereof extending in both longitudinal and transverse direction and being open at the bottom thereo=f,-said air chamber being provided with inlets at the fore end and air outlets at the aft end, and means for forcing air through the air inlets to the air chamber in adjustable quantities, so as to produce a longitudinal air flow in the air chamber, the air chamber having additional air inlets and air outlets at the port and starboard edges of the air chamber, and independent means for forcing -a stream of air through either the port or the starboard air inlets so as to produce a transverse air flow in the air chamber.

2. Ship according to claim 1 and having an anti-rolling tank, formed as a U-tube containing water, closed at its free upper ends, the air space above the Water in one of the tank legs being connected with the air chamber at one side edge, whereas the air space of the other tank leg is connected with the chamber at the other side edge.

References Cited in the tile of this patent UNITED STATES PATENTS France Dec. 22, 1956 

